Lecture 14 - Membrane transport + introduction to enzymes

Question 1

what is a chemical potential?

Answer 1

-the work required to maintain the concentration gradient

Question 2

when is there an electric potential?

Answer 2

-if ions are being transport + there is a charge difference between the inside and outside

Question 3

when does spontaneous diffusion occur?

Answer 3

-occurs naturally in the direction of negative overall delta G (transport along the gradient)

Question 4

what kind of transport requires energy?

Answer 4

active transport against the gradient

Question 5

what is valinomycin?

Answer 5

-an example of a carrier ionophore

Question 6

what does valinomycin do?

Answer 6

• coordinates and wraps around K+ ion
• help it diffuse through the membrane
• never has to leave the lipid interior

Question 7

Valinomycin is involved in what type of transport?

Answer 7

passive transport/facilitated/diffusion

Question 8

what are the 3 classifications of transport membranes?

Answer 8

1. active, passive, non-mediated
2. saturable vs. unsatruable
3. uniport, symport or antiport

Question 9

what is active transport?

Answer 9

-requires expenditure of free enegy

Question 10

what is passive transport?

Answer 10

also called facilitated diffusion (no energy)

Question 11

what is non-mediated transport

Answer 11

spontaneous diffusion

Question 12

when does a transport saturate?

Answer 12

-if its rate reaches a maximum when there are too many molecules (substrates) to transport

Question 13

what is an example of a saturated carrier?

Answer 13

valinomycin

Question 14

does non-mediated transport ever saturate?

Answer 14

no

Question 15

pores are usually _____

Answer 15

passive transporters

Question 16

what can toxins act as?

Answer 16

-certain bacteria produce toxins that act as pore in the cell membrane

Question 17

what is gramacidin A?

Answer 17

produced by bacillus brevis

• mediates uncontrolled transport of cations across cell membranes
• upsets normal concentration gradients

Question 18

other porin (in bacteria) or channel (in eukaryotes) proteins are required to ____

Answer 18

facilitate transport of ions or small molecules even in water

Question 19

what are aquaporin?

Answer 19

transports water in some bacteria or fungus at high rate into the cell

Question 20

what are 5 modes of selectivity for transport?

Answer 20

1. size
2. charge
3. coordination
4. gating
5. conformational charge

Question 21

size EX

Answer 21

aquaporin has narrow channel for H2O

Question 22

charge EX

Answer 22

Cl- ion charge positions alpha helices and -OH groups on Ser and Tyr side chains to attract the chloride ion

Question 23

coordination EX

Answer 23

• K+ and Na+ channels using different carbonyl groups on the mainchain to coordinate the two ions different
• strip away the H2O in their solvation shells

Question 24

gating EX

Answer 24

-K+ channel opens and closes, controlled by the membrane electrical potential

Question 25

conformational change EX

Answer 25

-glucose transporter accepts and releases its substrate by a conformational change

Question 26

how do primary active transports work?

Answer 26

they use free energy from ATP to carry out transport against the gradient

Question 27

what does the sodium potassium pump do?

Answer 27

maintains the potassium and sodium concentration gradients in cells by antiport active transport

Question 28

what is P-glycoprotein?

Answer 28

- over-expressed in multidrug resistant MMDR cancer cells | - ATPase that pumps many foreign substances out of cells

Question 29

what is Ca2+ ATPase?

Answer 29

pumps calcium ions out of the cytosol

Question 30

what is secondary active transport?

Answer 30

-couples the free energy derived from a primary process to drive a secondary transport

Question 31

what are 2 examples of secondary transport?

Answer 31

E. Coli uses electron transfer reactions the sodium conc. gradient derived from the Na+ K+ ATPase used to drive secondary symport glucose transport into the cell